Backpack



FIG. 1 is a perspective view of a backpack embodying my new design;

FIG. 2 is a rear view of the backpack of FIG. 1;

FIG. 3 is a front view of the backpack of FIG. 1;

FIG. 4 is a left side view of the backpack of FIG. 1;

FIG. 5 is a top view thereof of the backpack of FIG. 1; and,

FIG. 6 is a bottom view of the backpack of FIG. 1.

The broken lines showing straps in FIGS. 1-6 represent environmental matter and form no part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described herein. 